Gas barrier resins, for example, ethylene-vinyl alcohol copolymers (hereinafter, also abbreviated as EVOH) are materials having excellent oxygen barrier properties. Such resins can be melt-molded, and thus they are preferably used as a multilayer packaging material comprising a layer of such a resin laminated with a layer made of a thermoplastic resin (polyolefin, polyester, etc.) having excellent moisture resistance, excellent mechanical properties, and the like. However, the gas transmission of these gas barrier resins is not completely zero, and they transmit a non-negligible amount of gas. In order to reduce such transmission of gas, especially oxygen, which significantly affects the quality of a content of a packaged product, in particular the quality of food, or in order to absorb and remove oxygen that is already present inside a packaged product at the time of packaging its content, it is known to use an oxygen absorbent in a state of being mixed in a packaging material.
Compositions containing a thermoplastic resin having an unsaturated hydrocarbon, and a transition metal catalyst have been proposed as ingredients suitable for oxygen absorption.
For example, Patent Document 1 has disclosed an oxygen-absorbing resin composition using polyoctenylene as the thermoplastic resin. Such polyoctenylene is produced through ring-opening metathesis polymerization of cyclic olefin using a transition metal carbene complex catalyst such as a ruthenium compound. However, it is pointed out that, when used as a packaging material, such an oxygen-absorbing resin composition is decomposed and may generate an unpleasant odor as oxygen absorption proceeds. Therefore, there are demands for a further odor improvement for applications in which odorless packing is highly required.
Furthermore, Patent Document 2 has disclosed an oxygen-absorbing resin composition using polynorbornene as the thermoplastic resin. Such a thermoplastic resin is produced, for example, through ring-opening metathesis polymerization of norbornene using a ruthenium compound. However, it is pointed out that such an oxygen-absorbing resin composition is also decomposed and may generate an unpleasant odor as oxygen absorption. Therefore, there are demands for a development of an oxygen-absorbing resin composition that has excellent oxygen-absorbing properties, and enables further reduction of an unpleasant odor resulting from oxygen absorption.
Moreover, Non-Patent Document 1 has disclosed that poly(bicyclo[3.3.0]octa-2-en-6,8-diylidene) (hereinafter, also abbreviated as poly(dicyclopentadiene) or PDCPD) can be produced through ring-opening metathesis polymerization of dicyclopentadiene using a tungsten compound. However, it is not stated, for example, whether or not this material has oxygen-absorbing properties, whether or not this material is decomposed and generates an unpleasant odor as oxygen absorption proceeds, or the like.